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Radio Waves and Signals. Week 4. We imagine radio signals/waves travel as sine waves. The ripple of these waves are started by the vibration of an electron. The signal is produced in the circuits of the r adio, once the vibration leaves the radio through the antenna it becomes

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Presentation Transcript
slide2

We imagine radio signals/waves

travel as sine waves.

The ripple of these waves are started by

the vibration of an electron

slide3

The signal is produced in the

circuits of the radio, once

the vibration leaves the

radio through the

antennait becomes

a radio wave.

slide4

Radio waves are just one part

of the electromagnetic spectrum

slide5

An electromagnetic wave consists

of a vibrating

electric field

and a

vibrating

magnetic

field.

slide6

It is the electromagnetic wave

that carries the radio signal between the

transmitting

and

receiving

stations.

slide7

The EM wave oscillates in such a way to

mimic the signal that generated the wave.

slide8

A cycle is one complete vibration.

This diagram actually shows 3 cycles.

slide9

Wavelength (l) is the distance the wave

travels in 1 complete cycle

slide10

The number of vibrations per second

is the frequency.

What is the

frequency of

each wave?

1 second

2 Hz

10 Hz

Frequency is measured in Hertz (Hz):

1 vibration/sec is 1 Hz

slide11

AM stations broadcast in kilohertz (kHz)

1330 KVOL broadcasts at 1,330,000 Hz

FM stations broadcasts in megahertz (MHz)

96.5 KPEL broadcasts at 96,500,000 Hz

slide12

Test Question Alert!

What type of wave carries radio

signals between transmitting

and receiving stations?

Electromagnetic

slide13

Test Question Alert!

What is the name for the distance

a radio wave travels during

1 complete cycle?

Wavelength

slide14

Test Question Alert!

What term describes the number of times per second that an alternating current reverses direction.

frequency

slide15

In what unit is frequency measured?

Hertz

1

1

A Hertz is ____ vibration(s) per _____ second(s)

slide16

Test Question Alert!

What are the two components of a radio wave? (or any other wave in the electromagnetic

spectrum)

Electric and

magnetic fields

slide17

All radio waves travel at the speed

of light (c) through a particular type

of medium.

The speed of light through

space is 300,000,000 m/s

slide18

Since all radio waves travel at the speed of light no matter what their frequency happens to be the following is true:

When length increases

then frequency decreases

or

when length decreases

then frequency increases.

slide19

Radio waves can be referred to by

wavelength or frequency because

the two are related by the speed of light.

c

f

l

slide20

A wave with a length of 2 m means

it has a frequency of 150,000,000 Hz

because

300,000,000 / 150,000,000 = 2

This frequency typically would be referred to as 150 MHz

slide21

The formula for converting frequency to wavelength in meters is :

Wavelength in meters = 300 divided by frequency in megahertz.

300

l

in m

f in

MHz

slide22

To convert frequency to wavelength in meters divide 300 by frequency in MHz.

96.5 KPEL broadcasts at 96.5 MHz so the length of the waves is 300/96.5. The waves are approximately 3 meters in length.

slide23

What property does wavelength refer to?

The distance a wave travels during

1 complete cycle.

slide24

How fast does a radio wave travel?

(Two acceptable ways to answer)

Speed of light

or

300,000,000 meters/second

slide25

Describe the relationship between

wavelength and frequency.

inverse

wavelength frequency

or

wavelength frequency

slide26

What is the formula for converting

frequency into wave length (in meters)?

300 / Mhz

slide29

All types of radio frequency signals are referred to by the abbreviation RF, but for convenience the entire range is spilt into sub-ranges.

3000 MHZ

slide30

Communications at VHF and UHF

are generally “line of sight” communications.

That is they travel directly from the

transmitting station to the receiving

station.

Normally used for local communication.

slide31

Direct (not via a repeater) UHF signals are

rarely heard from stations outside your

local coverage area because UHF signals

are not reflected by the ionosphere.

slide32

The radio horizon is the distance at which radio

signals between two point are blocked by the

curvature of the Earth.

The radio horizon is somewhat farther than the

visual horizon because the earth seems less

curved to radio waves than light waves.

slide33

When using a hand-held transceiver inside a building you might want to choose to operate in a UHF band.

  • UHF signals are often more effective from inside buildings than VHF signals because the shorter
  • wavelengthallows them to more easily penetrate the structure of buildings.
slide34

Knife-edge propagation is the term used to describe when signals are partially refracted around solid objectsexhibiting sharp edges.

  • You might be able to use this phenomenon
  • to get your signal around a building in an
  • urban setting.
slide35

What is the name assigned to each

of these frequency ranges?

3 – 30 MHz

30 – 300 MHZ

300 – 3000 MHz

slide36

Why are UHF frequencies usually

limited to local communications?

UHF signals are not reflected

by the ionosphere.

slide37

What do we call the distance at which

radio signals are blocked by the curvature

of the Earth?

Radio Horizon

slide38

Why is the radio horizon somewhat farther that the visual line of sight distance between two stations?

The earth seems less curved

to radio waves than to

light waves.

slide39

Why should you choose to use

frequencies in the UHF band when using

a hand-held receiver inside a building?

The shorter waves length allows them to

more easily penetrate the structure of

the building.

slide40

What do we call the phenomenon in which

signals are partially refracted (bent) around

solid objects with sharp edges?

Knife-edge propagation